A network called a body area network is known which is formed in a human body as a wireless network. In a body area network, a hub which functions as a central device and nodes which function as terminal devices are attached to a human body and communication is performed between the hub and nodes.
There is a mechanism in which a schedule-based access scheme and a non-schedule-based access scheme, for example CSMA (Carrier Sense Multiple Access), share the same frequency on a time basis. One known schedule-based access scheme is TDMA (Time Division Multiple Access)-based access scheme, which is a simple access scheme and therefore desirable in terms of reduction of power consumption in nodes.
In TDMA, in order to assign a time slot to each node in advance, basically slot assignment information for each node may be inserted in a beacon signal as an announcement signal, such as a beacon signal, which is periodically transmitted at constant intervals. In this case, each node receives the beacon signal, identifies the slot assigned to the node on the basis of the slot assignment information contained in the beacon signal, and performs transmission and reception using the identified slot.
In this method, when a node fails to receive the beacon signal in which the slot assignment information is inserted, a collision can occur because plural nodes may use the same slot. In order to avoid such collision, a mechanism has been proposed in which each node basically needs to always perform transmission in a slot assigned to the node and, only if the node fails to receive the beacon signal immediately before the slot, the node does not perform transmission in the assigned slot, thereby notifying the hub that the node has failed to receive the beacon signal.
However, the proposed mechanism has a problem that nodes consume higher power because each node needs to transmit in every slot assigned to the node. In addition, because the hub needs to insert assignment information for each node into a beacon signal that the hub periodically transmits, the beacon signal length is increased and the power consumption for receiving the beacon signal is increased accordingly.